Harmonization of chaos into a soliton in Kerr frequency combs

Soliton synchronization in microresonators with a modulated pump

Microresonator frequency comb generation from Kerr solitons has become a cutting edge technology, but challenges remain in creating, maintaining, and controlling the solitons. Pump modulation and dual pumping are promising techniques for meeting these challenges. Here we derive the equation of motion of solitons interacting with a modulated pump in the framework of synchronization theory. It implies that the soliton repetition rate locks to the modulation frequency whenever the latter is within a locking range of frequencies around an integer multiple of the free spectral range of the microresonator. We calculate explicitly, numerically, and in perturbation theory the width of the locking range as a function of the amplitude and frequency of the pump and the modulation phase. We show that a highly red-detuned, strong pump that is amplitude-modulated provides the best conditions for entrainment, and that the width of the locking range is proportional to the square of the modulation frequency, limiting the effectiveness of RF modulation as an entrainment method.

Kerr soliton frequency comb generation by tuning the coupling coefficient in coupled nonlinear microcavities

Kerr soliton frequency comb generation in nonlinear microcavities with compact configurations are promising on-chip sources. Current Kerr comb generation by using a single microcavity with a tunable CW pump laser or high-power femtosecond pulse pump are difficult to be integrated on chip. In this paper, we propose an on-chip soliton comb generation scheme by tuning the coupling coefficient of two coupled microcavities instead of tuning the wavelength of the cw pump laser or using a pulsed pump laser in a single microcavity. The two microcavities are assumed to be identical. We showed by numerical simulation that Kerr comb generation is possible in both the blue and red detuned regions of the main microcavity in the coupled cavity system. We further found that the range and boundary of the soliton generation region of the couple microcavities depend on the coupling coefficient between the coupled cavities. To ensure that the modes being coupled have identical optical paths, we designed a Sagnac loop structure which couples the clockwise and counterclockwise modes in a single microcavity and demonstrated Kerr comb generation in both the blue and red detuned regions by tuning the coupling coefficient. The proposed Kerr comb generation scheme can be utilized for chip-scale integrated soliton comb sources, which will contribute to the development of on-chip applications.

Dissipative Kerr solitons, breathers, and chimera states in coherently driven passive cavities with parabolic potential

We analyze the stability and dynamics of dissipative Kerr solitons (DKSs) in the presence of a parabolic potential. This potential stabilizes oscillatory and chaotic regimes, favoring the generation of static DKSs. Furthermore, the potential induces the emergence of new dissipative structures, such as asymmetric breathers and chimera-like states. Based on a mode decomposition of these states, we unveil the underlying modal interactions.

Dynamics of cavity soliton driven by chirped optical pulses in Kerr resonators

Recent researches have demonstrated that pulsed driving is an effective method to increase the temporal overlap between cavity soliton (CS) and pump field, thereby increasing the pump-to-comb conversion efficiency. The amplitude-modulated inhomogeneity of the background wave causes the solitons to drift toward edges of the driving pulse. To eliminate the multiple temporal trapping positions, induced by the spontaneous symmetry breaking, we propose the chirped pulse driving for deterministic single soliton generation. We theoretically explain the physical mechanism of the chirp pulse driving, as the combination of amplitude and phase modulation. Our numerical simulations demonstrate the chirp is responsible for the single soliton generation. A detailed investigation for dynamics of CSs sustained by chirped pulses, shows the recovery of spontaneous symmetry breaking. In addition, the desynchronized chirped pulse driving is also considered here. Considering a weak chirp parameter, the desynchronization-dependent trapping position diagram is divided into multiple areas including two CSs, a single CS, two oscillating CSs, and no CS. With a sufficient chirp parameter considered, the trapping position curve becomes a monotonous function of the desynchronized drift velocity, which indicates deterministic single soliton generation.

Microsphere-Based Optical Frequency Comb Generator for 200 GHz Spaced WDM Data Transmission System

Optical frequency comb (OFC) generators based on whispering gallery mode (WGM) microresonators have a massive potential to ensure spectral and energy efficiency in wavelength-division multiplexing (WDM) telecommunication systems. The use of silica microspheres for telecommunication applications has hardly been studied but could be promising. We propose, investigate, and optimize numerically a simple design of a silica microsphere-based OFC generator in the C-band with a free spectral range of 200 GHz and simulate its implementation to provide 4-channel 200 GHz spaced WDM data transmission system. We calculate microsphere characteristics such as WGM eigenfrequencies, dispersion, nonlinear Kerr coefficient with allowance for thermo-optical effects, and simulate OFC generation in the regime of a stable dissipative Kerr soliton. We show that by employing generated OFC lines as optical carriers for WDM data transmission, it is possible to ensure error-free data transmission with a bit error rate (BER) of 4.5 × 10−30, providing a total of 40 Gbit/s of transmission speed on four channels.

Thermally stable access to microresonator solitons via slow pump modulation

Temporal dissipative Kerr solitons (DKSs) in microresonators provide ultra-short optical pulses and low-noise frequency combs with gigahertz to terahertz repetition rates. Owing to their unique properties, they have found application in fields, including optical communications, rapid laser ranging, and optical precision spectroscopy. However, due to the thermal instability encountered when entering the DKS regime, the stable generation of solitons remains challenging for many systems and usually requires rapid actuation of the pump laser detuning, pulsed driving, additional lasers, a particular mode structure and/or active feedback loops to stabilize the system. Here we show that slow pump modulation can remove the thermal instability and enable passively stable soliton states that can be readily accessed via arbitrarily slow laser tuning, thereby greatly reducing the technical complexity of stable DKS generation.

Bichromatic pumping in mid-infrared microresonator frequency combs with higher-order dispersion

Integrated microresonator-based mid-infrared frequency combs based on III-V semiconductors exhibit pronounced higher-order group velocity dispersion that can make it difficult to achieve stable output. One way to stabilize multiple solitons and their repetition rate is to pump simultaneously at two nearby comb lines. Two-color (or bichromatic) pumping also promises to boost the relatively low conversion efficiencies of single-soliton combs. We present simulations showing that, for a realistic InGaAs/InP ridge waveguide, the stabilization effect occurs over only a limited range of pump power and detuning parameters. We map out the parameter ranges for various regimes of operation in terms of the pump power and detuning and determine that the regimes converge quickly as the dispersion is truncated to progressively higher orders.

Imaging soliton dynamics in optical microcavities

Solitons are self-sustained wavepackets that occur in many physical systems. Their recent demonstration in optical microresonators has provided a new platform for the study of nonlinear optical physics with practical implications for miniaturization of time standards, spectroscopy tools, and frequency metrology systems. However, despite its importance to the understanding of soliton physics, as well as development of new applications, imaging the rich dynamical behavior of solitons in microcavities has not been possible. These phenomena require a difficult combination of high-temporal-resolution and long-record-length in order to capture the evolving trajectories of closely spaced microcavity solitons. Here, an imaging method is demonstrated that visualizes soliton motion with sub-picosecond resolution over arbitrary time spans. A wide range of complex soliton transient behavior are characterized in the temporal or spectral domain, including soliton formation, collisions, spectral breathing, and soliton decay. This method can serve as a visualization tool for developing new soliton applications and understanding complex soliton physics in microcavities.

Deterministic generation of single soliton Kerr frequency comb in microresonators by a single shot pulsed trigger

Kerr soliton frequency comb generation in monolithic microresonators recently attracted great interests as it enables chip-scale few-cycle pulse generation at microwave rates with smooth octave-spanning spectra for self-referencing. Such versatile platform finds significant applications in dual-comb spectroscopy, low-noise optical frequency synthesis, coherent communication systems, etc. However, it still remains challenging to straightforwardly and deterministically generate and sustain the single-soliton state in microresonators. In this paper, we propose and theoretically demonstrate the excitation of single-soliton Kerr frequency comb by seeding the continuous-wave driven nonlinear microcavity with a pulsed trigger. Unlike the mostly adopted frequency tuning scheme reported so far, we show that an energetic single shot pulse can trigger the single-soliton state deterministically without experiencing any unstable or chaotic states. Neither the pump frequency nor the cavity resonance is required to be tuned. The generated mode-locked single-soliton Kerr comb is robust and insensitive to perturbations. Even when the thermal effect induced by the absorption of the intracavity light is taken into account, the proposed single pulse trigger approach remains valid without requiring any thermal compensation means.

Addressing temporal Kerr cavity solitons with a single pulse of intensity modulation

We experimentally and numerically study the use of intensity modulation for the controlled addressing of temporal Kerr cavity solitons (CSs). Using a coherently driven fiber ring resonator, we demonstrate that a single temporally broad intensity modulation pulse applied on the cavity driving field permits systematic and efficient writing and erasing of ultrashort cavity solitons. We use numerical simulations based on the mean-field Lugiato-Lefever model to investigate the addressing dynamics, and present a simple physical description of the underlying physics.

Parametric control of thermal self-pulsation in micro-cavities

We propose a scheme for bifurcation control in micro-cavities based on the interplay between the ultrafast Kerr effect and a slow nonlinearity, such as thermo-optical, free-carriers-induced, or opto-mechanical one. We demonstrate that Hopf bifurcations can be efficiently controlled with a low energy signal via four-wave mixing. Our results show that new strategies are possible for designing efficient micro-cavity-based oscillators and sensors. Moreover, they provide new understanding of the effect of coherent wave mixing in the thermal stability regions of optical micro-cavities, fundamental for micro-resonator-based applications in communications, sensing, and metrology, including optical micro-combs.